Immune responses in adult female volunteers during the bed-rest model of spaceflight: Antibodies and cytokines

Background It is unknown whether a prolonged period of bed rest will affect human immune responses, particularly in female subjects. Objective We sought to measure immune responses in adult female subjects exposed to prolonged bed rest. Methods Adult (25-40 years) female volunteers (n = 24) were maintained in a supine (6° tilt) head-down bed-rest (HDBR) position for 60 days: 8 with HDBR only, 8 with HDBR and regular muscular exercise, and 8 with HDBR and dietary protein supplementation. Subjects were immunized with bacteriophage φX-174. Antibody production and plasma cytokine levels were determined. Results The rate of primary antibody production of the HDBR plus exercise group increased faster ( P = .01) and to a higher level versus that of the HDBR-only group ( P = .03) and that of the HDBR plus diet group (trend P = .08). The rates of secondary antibody production between the 3 groups were similar, but the level of antibody in the HDBR plus exercise group remained higher versus that in the HDBR-only group ( P = .03). Both the HDBR ( P = .001) and HDBR plus diet ( P = .02) groups had time-related progressive increases in TNF-α receptor levels, but the HDBR plus exercise group remained at baseline. The HDBR plus exercise group experienced an acute increase in IL-1 receptor antagonist levels versus the HDBR ( P = .02) and the HDBR plus diet ( P = .02) groups, with similar increases in RANTES levels. Conclusions The exercise countermeasure accelerated primary antibody production and increased antibody levels to bacteriophage φX-174 and also opposed the potentially harmful effects of increased TNF-α levels caused by prolonged bed rest, possibly by activating the anti-inflammatory cytokine IL-1 receptor antagonist and the chemotactic factor RANTES.